In some apparatuses, sliding movement between two members is required under different conditions such as the state of being lubricated as well as that without lubrication, or in the dry state as well as the wet state.
A typical example of such apparatus may be bearings employed in a pump of a vertical shaft type or an inclined shaft type. In such a pump, a motor is usually disposed at a high position above the water level and a long shaft extends from the motor to a pump section submerged within the water. The long shaft is intermediately supported by bearings and such bearings are to be lubricated for rotatably supporting the shaft, the lubrication being usually effected by self-pumped water or water supplied externally from an auxiliary source. Therefore, such bearings are kept in the dry state when the pump is not operating. On the other hand, if one wishes to operate the pump, it would be necessary to supply water to the bearings in advance of actuating the motor, since otherwise the bearings, which are usually made of rubber, would seize.
Therefore, it has been desired to provide a novel combination of sliding members which permits relative sliding movement in the dry state as well as the wet state.
Heretofore, bearings made of graphite, sintered alloy containing graphite or fluorine-containing polymers (Trade Mark: Teflon) have been available which permit the initiation of rotation without lubrication. However, such bearings are easily and quickly worn compared to the conventional rubber bearings used in this type of pump.
Also, there are other types of bearings such as an oil impregnated type which allows rotation without supplying lubricant from outside. However, this type of bearing is not suitable for use in the pump discussed above in both the dry and wet states.
Further, in addition to the problem regarding abrasion, corrosion has also been a problem in the bearings used in the pumps described above, the corrosion being mostly due to the contact potential between the different metals.
It is also evident that a conventional roller bearing cannot withstand use under both dry and wet states.
Therefore, it has been desired to obtain a novel combination of sliding members which is capable of effecting smooth movement between each member in both the dry and wet states, and has a long service life.